1. Field of the Invention
The present invention relates to an anterior segment surgical apparatus in ocular surgery, and more particularly to a laser apparatus having application in cataract surgery for capsulorhexis, i.e. the cutting of a capsulotomy in the anterior capsule of a lens of an eye, and for other procedures in cataract surgery. The apparatus may also be used in surgical procedures for the cornea and posterior capsule.
2. Description of Related Art
The standard procedure for correcting vision loss due to cataracts is to remove the natural lens and to replace it with a prosthetic lens. In typical cataract surgery, an initial incision is made into the cornea of the eye and then the surgeon creates a circular opening in the anterior lens capsule. This is referred to as a capsulotomy. Producing the circular opening is often a critically demanding procedure. It is also known as an anterior lens capsulectomy once the circular fragment of the lens capsule is removed. The latter name is in reference to the analogous posterior lens capsulotomy, which has come to be well known in surgery practice and which involves the use of a pulsed YAG laser. Once the anterior capsulotomy is completed, the natural lens cortex is extracted by breaking it up into small pieces, which are drawn through the initial opening. As this procedure and pseudophakic materials have improved over time, the initial incision has become smaller, such that it is now normally less than 3 mm. Reducing the initial incision has improved the surgical outcome but has placed higher and higher demands on the surgeon and the surgical instruments that pass through the initial incision.
The anterior capsulotomy portion of cataract surgery as defined above preferably results in a circular opening of a selected diameter and without radial tears. Ideally, it has smooth edges. The usual instruments used by the surgeon are the cystotome or forceps, which are used to basically puncture and tear the capsule tissue to produce the opening. The results are at best imperfect circles, and sometimes radial tears or other adverse events occur. For advanced lens technologies, it is particularly important to consistently produce a smooth, intact and round capsulotomy without radial tears in the capsule.
Laser techniques that have been attempted include the application of the well established posterior capsulotomy YAG laser operating with a 1064 nm wavelength. In 1981, Aron-Rosa reported on laser opening of the anterior capsule from 1 to 24 hours before extra-capsular cataract surgery. (Am Intra-ocular Implant Soc J, Vol 7, p. 332, 1981) It was shown that by depositing one laser pulse at a time aimed at the anterior lens capsule, a rudimentary capsulectomy could be produced, but with complications in some cases. The complications included high intraocular pressures caused by the laser pulse shock wave, edge roughness and irregular shaped capsulectomies. Unintended exposure of the retina to hazardous levels of laser radiation can occur if the pulse is not blocked by a necessary plasma breakdown process at the focal point at the lens anterior capsule. Other disadvantages include the tedium of depositing a few hundred pulses, one pulse at a time, a situation that can contribute to operator error. For these reasons, such a technique has not been accepted by surgeons.
In 1982, Horn et al reported on the use of a “cool” laser operating at a 1220 nm wavelength. (Am Intra-ocular Implant Soc J, Vol 8, 1982) The intended objective of moving from the 1064 nm wavelength to the 1220 nm wavelength was to cut power requirements 100-fold and avoid jeopardizing the retina when doing anterior chamber surgical treatments. Horn et al used a very elaborate laser system to achieve the preferred wavelength: a Nd:YAG pump laser source was converted to 532 nm, which was then used to pump a 600 nm dye laser, and finally converted to a 1220 nm laser source by means of a high-pressure hydrogen gas cell. The work was done on rabbit subjects. No report of follow-on work was found.
Various reports of the use of lasers in cataract surgery have appeared in more recent years. In 2009, a LenSx femtosecond laser received approval from the U.S. Food and Drug Administration for creation of the capsulorhexis during cataract surgery. (Rev of Ophthalmology, October 2009, p. 29) A recent patent application by the same company discussed the use of a pulsed laser for: photodisruption of a portion of a targeted region in the lens of an eye, for making an incision in the capsule of the lens and for making an incision in the cornea of the eye (WO 2009/039302 A2). These lasers normally emit at wavelengths shorter than 1000 nm, which raises their potential of affecting the sensitive retina. The femtosecond lasers are also expensive and require substantial maintenance.
What is needed is a pulsed laser system that can be used to form the capsulorhexis during cataract surgery that is effective and economical, so that it can be made widely available for use by surgeons, and that employs a wavelength having preferred absorption properties in the tissue of an eye.